In high speed supercomputers, such as the types manufactured by Cray Research, Inc., the assignee of the present invention, banks of printed circuit boards containing integrated circuit devices are used to complete the circuitry which enables high speed calculations to be performed. Each semiconductor chip may exhibit different speed characteristics, even ones manufactured on the same wafer. Therefore, prior to beginning actual production of a supercomputer, it is important that each integrated circuit is tested to ensure that none of the circuits contain electrical open or short circuits and to ensure the circuit is able to run at the high clock speeds that the supercomputers require.
Some variations of errors on an integrated circuit will only be detectable with at-speed testing. At-speed or AC testing refers to high-speed testing the integrated circuit at or near the same speed it will operate in the computer. A testing method must be capable of conducting the tests at speeds up to 1GHz. Also, the testing device must not introduce any parasitics. At high frequencies, if parasitics were introduced, the testing device would not record accurate data. From a cost standpoint, it is important that such testing is conducted quickly and efficiently. It is clear that there has existed an unfilled need in the prior art for an at-speed integrated circuit testing apparatus and method to ensure the actual performance of the circuit meets the predetermined specifications.